Beneficiation of low-grade, goethite-rich iron ore using microwave-assisted magnetizing roasting

Microwave-assisted reduction roasting of a goethite-rich, reject iron ore waste stream (−2 mm) was used to produce a high-grade concentrate. Reduction roast experiments were conducted at 370 °C, 450 °C, 600 °C and 1000 °C under gas atmospheres of 30:70 and 40:60 CO/CO2, with a soak time of 20 min. Goethite was converted to hematite above 370 °C under both gas mixtures while at the higher roasting temperatures, increasing amounts of magnetite formed. Roasting conditions for the best conversion of goethite to synthetic magnetite were 600 °C in a gas atmosphere of 40:60 CO/CO2, with a soak time of 20 min. Laboratory-based magnetic separations in a Davis tube indicated that a blast furnace grade (+62 wt% Fe) pellet concentrate could be produced with an acceptable iron recovery of > 88 wt%. Under both gas atmospheres, a higher reduction temperature of 1000 °C achieved a greater conversion of goethite to magnetite but resulted in over-reduction and the generation of wüstite, fayalite and Fe-rich spinel phases with different magnetic susceptibilities that are expected to make subsequent beneficiation difficult. Further processing to optimize the microwave-assisted magnetizing roast and the magnetic separation conditions can be expected to maximize the efficiency of upgrading the iron content in low grade goethite-rich iron ores.